Thermometers are extremely important in the candy-making process because slight variances in temperature can make the difference between a successful batch of candy and one that's inedible. Two essential thermometers to have when you make candy are a candy thermometer and a chocolate thermometer.
If you visit a candy kitchen, you'll see a variety of types of thermometers — some quite expensive and elaborate. Fancier thermometers give digital readouts quickly and accurately. Some thermometers take readings by laser, but they don't penetrate beyond the surface of the candy, so they're less reliable for actual temperature readings. If you plan to make candy at home, a fairly inexpensive thermometer will do just fine; it just needs to give you accurate temperatures when you cook. However, if you plan to do a lot of candy making, invest in quality thermometers because you want them to last through many, many uses.
Candy thermometers
Purchase a candy thermometer that clips to the side of a pot (see Figure 1) because you'll need to clip the thermometer on the pot during the cooking process to measure the temperature of your batch.
Figure 1: You can attach a candy thermometer to a pot with a clip.
When clipping the thermometer to your pot, make sure that the tip doesn't touch the bottom of the pot because the thermometer will give you a false reading.
You can purchase basic or more sophisticated candy thermometers. Your decision depends on how often you plan to make candy. If you plan to make candy a lot, consider investing a little more money in a quality, just as you would with any kitchen utensil you use often. Prices can range from $12 for a simple thermometer to $35 for a digital thermometer.
To satisfy all your candy-making needs, look for a candy thermometer that measures a range from 100 degrees to 400 degrees; most thermometers have graduations of 5 degrees. Better candy thermometers have graduations of 2 degrees, which allow you to measure your batch's temperature more accurately. Some commercial thermometers have more detailed graduations within a specific range, perhaps from 160 degrees to 270 degrees, but these thermometers are designed for specific candies.
Chocolate thermometers
In its liquid state, chocolate exists in a range from 82 degrees to about 115 degrees, and this range is where you work all your candy-making magic. Your chocolate may occasionally reach 120 degrees, but watch out — you can easily scorch your chocolate then.
Because of the low temperature range of melted chocolate, chocolate thermometers are marked in 1-degree graduations from about 40 or 50 degrees to 130 degrees. (If your chocolate reaches 130 degrees, you have a problem.)
A simple chocolate thermometer costs between $12 and $15. Most chocolate thermometers are glass cylinders (see Figure 2), so when you're finished using your thermometer, clean it carefully with slightly warm water and store it where it won't get broken.
Figure 2: A chocolate thermometer is usually made of glass.
For a few dollars more, you can purchase a digital thermometer. This type of chocolate thermometer has a metal probe that you insert into a solution that gives an accurate reading for boiling cream and tempered chocolate.